(1) Field of the Invention
The present invention relates to an electrical power flow control method for hybrid systems. In particular, the present invention relates to the control of electrical power flow in hybrid electric (both plug-in and non plug-in) vehicles.
(2) Description of Related Art
Global warming and the prospect of depleting fossil fuels have motivated many industries to redesign vehicles that utilize alternative energy sources instead of the conventional internal combustion engine. There are several advantages to using alternative energy vehicles, such as reducing emissions in the atmosphere, reducing our dependence on oil both at home and abroad, and reducing cost to the user because the need to purchase gasoline at rising costs is lessened or eliminated altogether.
Hybrid vehicles use a conventional internal combustion engine along with an electric motor supplied with power through a battery. The battery is continuously recharged by the internal combustion engine, such as with a connection to a generator. Hybrids can operate in one of two ways. First, a hybrid can operate in a parallel design, wherein an energy conversion unit and electric propulsion system are connected directly to the vehicle's wheels. The internal combustion engine is used for highway driving whereas the electric motor provides added power when an energy boost is needed. Second, a hybrid can operate in a series design, wherein the internal combustion engine is connected to the generator to produce electricity to charge the battery of the electric motor. The electric motor then powers the wheels of the vehicle. Many hybrid vehicles are also able to use regenerative braking to store and convert energy normally lost through braking and deceleration into useful power.
Plug-in vehicles essentially are hybrids with the added advantage of a larger battery and the ability to recharge externally at a power source.
Fuel cell electric vehicles (FCEV) are able to generate their own electricity through the use of hydrogen reacting with oxygen in a fuel cell, and the electricity can be used to charge a battery which in turn powers an electric motor. The hydrogen can be present in the cell or can be converted from another fuel. The hydrogen produced can also be stored within gas tanks in the car. The fuel cell produces average power required to drive the vehicle on highway while batteries and ultra-capacitors provide transient power. FCEVs have virtually no emissions.
Plug-in vehicles and FCEVs are drawing tremendous attention in motor vehicle companies because of their potential in reducing dependence on oil and impact on the environment. However, both systems have major disadvantages. Plug-in vehicles have limitations on distance coverage, and fuel cells are very expensive, preventing widespread utilization in vehicles.
There is a need for better utilization of the existing energy sources in FCEVs by taking advantage of the unique charging/discharging properties of each source to maximize its capacities. The present invention accomplishes this through a systematic method of establishing component values and determining power distribution.